1. Field of the Invention
The present invention relates to a method and to an apparatus for three-dimensional testing of printed circuit boards on the basis of identified, spatial surface coordinates for the recognition of defects at the structures in (1) the microscopic domain on the basis of a planar, local evaluation window and current calculation of cross sectional areas; (2) the microscopic domain on the basis of a reference/actual value comparison within predetermined grid fields.
2. Description of the Prior Art
With increasing miniaturization of the structures on interconnects, the width of the interconnects is approaching the height of the interconnects. Since the electrical properties of the interconnects are critically determined by their cross sections, the height must also be checked in addition to the width in order to guarantee the required cross section. Current, automated methods are largely optical inspection systems that work with two-dimensional image evaluation. For testing structures that lie in the range of 10.sup.-5 m, both a high resolution in the planar form and in the three-dimensional form are important. One possibility of acquiring the surface structures is scanning the surface with laser triangulation. The optical scan beam generated by the laser unit is thereby picked up by a topically resolving receiver. Such optical receivers are referred to as position-sensitive photodetectors.
The inspection systems that are currently commercially available are affected by the following deficiencies:
the height resolution is too low, for example, only three height steps;
the processing speed is too low for current needs; and
the manipulation is too complicated.